DNA Soaks Up Sun's Rays

November 20, 2008

By Dr. Fazale Rana

DNA Optimized for Photostability, Adds to the Evidence for Design

About ten years ago my family and I moved from Ohio to sunny Southern California. I don’t think I could ever go back. I have no desire to experience ever again the frigid winters and humid summers that are major parts of living in the Midwest.

The year-round beautiful weather in the “southland” makes it possible to enjoy many carefree hours outdoors. But it also prompts some concerns about spending too much time in the sun. Soaking up too many of the Sun’s harmful rays can cause long-term damage to the skin—unless, of course, one lathers on the sunscreen.

Like Southern Californian sun “worshippers,” DNA also faces problems with short wavelength UV-radiation from the sun. This radiation can damage this all-important biomolecule. Fortunately, biochemists have discovered that DNA has unusual photostability. Scientists believe that specific structural features of DNA make it resistant to the harmful effects of the sun. It’s as if DNA has its own built-in sunscreen.

New research has uncovered some of the specific aspects of DNA structure that contribute to its unusual photostability, and—with this insight—add to the weight of evidence that biochemical systems are the work of a Creator.

The Structure of DNA

DNA consists of chain-like molecules known as polynucleotides. Two polynucleotide chains align in an antiparallel fashion to form a DNA molecule. (The two strands are arranged parallel to one another with the starting point of one strand in the polynucleotide duplex located next to the ending point of the other strand and vice versa.) The paired polynucleotide chains twist around each other to form the well-known DNA double helix. The cell’s machinery forms polynucleotide chains by linking together four different subunit molecules called nucleotides. The nucleotides used to build DNA chains are adenosine, guanosine, cytidine, and thymidine, famously abbreviated A, G, C, and T, respectively.

The nucleotide molecules that make up the strands of DNA are, in turn, complex molecules consisting of both a phosphate moiety, and a nucleobase (either adenine, guanine, cytosine, or thymine) joined to a 5-carbon sugar (deoxyribose).

Repeatedly linking the phosphate group of one nucleotide to the deoxyribose unit of another nucleotide forms the backbone of the DNA strand. The nucleobases extend as side chains from the backbone of the DNA molecule and serve as interaction points when the two DNA strands align and twist to form the double helix.

When the two DNA strands align, the adenosine (A) side chains of one strand always pair with thymidine (T) side chains from the other strand. Likewise, the guanosine (G) side chains from one DNA strand always pair with cytidine (C) side chains from the other strand.

The Photostability of DNA

As I pointed out in chapter seven of The Cell’s Design, biochemists have known for a while that the particular nucleobases found in DNA display ideal photophysical properties. Even though DNA routinely experiences photophysical damage, it could be far worse. It turns out that the optical properties of the bases found in nature minimize UV-induced damage. These nucleobases maximally absorb UV-radiation at the same wavelengths that are most effectively shielded by ozone. Moreover, the chemical structures of the nucleobases of DNA allow the UV-radiation to be efficiently radiated away after it has been absorbed, restricting the opportunity for damage.

To gain further insight into the structural features of DNA that contribute to its photostability, researchers from Germany prepared a number of model DNA compounds. It turns out that the molecular interactions that promote the pairing of the side groups in the DNA duplex help dissipate absorbed light energy. Variation of the nucleotide sequences in the strands of DNA also plays a role in photostability. This variability prevents long-lived excited states from forming when UV-radiation is absorbed by DNA.

It appears that DNA has been designed to have optimal photostability. This property is critical for DNA’s role in the cell as a data storage system. DNA harbors the information needed for the cell’s machinery to make proteins. It also houses the genetic information passed on to subsequent generations. If DNA isn’t stable, then the information it harbors will become distorted or lost. This will have disastrous consequences for the cell’s day-to-day operations and make long-term survival of life impossible.

As I discuss in The Cell’s Design, photostability is not the only feature of DNA that has been optimized. Other chemical and biochemical features appear to be carefully chosen to ensure its stability; again, a necessary property for a molecule that harbors the genetic information.

Optimized biochemical systems comprise evidence for biochemical intelligent design. Optimization of an engineered system doesn’t just happen—it results from engineers carefully optimizing their designs. It requires forethought, planning, and careful attention to detail. In the same way, the optimized features of DNA logically point to the work of a Divine engineer. It appears as if someone carefully designed the structure of DNA to spend many long hours in the sun.

Subjects:
Biochemical Design

Dr. Fazale Rana

In 1999, I left my position in R&D at a Fortune 500 company to join Reasons to Believe because I felt the most important thing I could do as a scientist is to communicate to skeptics and believers alike the powerful scientific evidence—evidence that is being uncovered day after day—for God’s existence and the reliability of Scripture. Read more about Dr. Fazale Rana

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